POLAR VIBRATIONAL MODES IN AG3ASS3 CRYSTALS

Abstract Reflectivity spectra of Ag 3 AsS 3 crystals have been investigated in the range from 50 to 4000 cm −1 for E ∥÷ c and E ⊥ c polarizations, and practically all expected vibrational modes of A 1 and E symmetry have been found. Phonon parameters, i.e. frequencies of LO and TO modes, longitudinal-transverse splitting and deilectric constants e χ and e 0 are determined. Effective ionic charges of Ag, As and S ions and their anisotropy are estimated.